C - C++ - web assembly

Compile new C/C++ module for WASM

  1. Get Emscripten SDK https://emscripten.org/docs/getting_started/downloads.html

Call C function from emscripten html module 

document.querySelector('.mybutton')
    .addEventListener('click', function() {
        alert('check console');
        var result = Module.ccall(
            'myFunction',  // name of C function
            null,  // return type
            null,  // argument types
            null  // arguments
        );
    });

Compile custom function defined in C 

# Use "Using C++ code as C code" example for how to define functions
# Note that we need to compile with NO_EXIT_RUNTIME, which is necessary as otherwise when main() exits the runtime would be shut down — necessary for proper C emulation, e.g., atexits are called — and it wouldn't be valid to call compiled code.
emcc -o hello3.html hello3.c -O3 --shell-file html_template/shell_minimal.html -s NO_EXIT_RUNTIME=1 -s "EXPORTED_RUNTIME_METHODS=['ccall']"

Using C++ code as C code 

Note: We are including the #ifdef blocks so that if you are trying to include this in C++ code, the example will still work. Due to C versus C++ name mangling rules, this would otherwise break, but here we are setting it so that it treats it as an external C function if you are using C++.
#include <stdio.h>
#include <emscripten/emscripten.h>

int main() {
    printf("Hello World\n");
}

#ifdef __cplusplus
extern "C" {
#endif

EMSCRIPTEN_KEEPALIVE void myFunction(int argc, char ** argv) {
    printf("MyFunction Called\n");
}

#ifdef __cplusplus
}
#endif

Stop Emscripten from elminating function as dead code 

# By default, Emscripten-generated code always just calls the main() function, and other functions are eliminated as dead code. Putting EMSCRIPTEN_KEEPALIVE before a function name stops this from happening. You also need to import the emscripten.h library to use EMSCRIPTEN_KEEPALIVE.

#include <emscripten/emscripten.h>

EMSCRIPTEN_KEEPALIVE void myFunction(int argc, char ** argv) {
    printf("MyFunction Called\n");
}